That pic right there is of a model, I think. But there are special light textures. They are basically "light" with an alpha channel or transparency or something... You put that texture (it must be a shader file too) on the brush, and put nodraw on the top and bottom.

Hey I was wanting to do a similar effect, I had one working in a different map but then it quit working... but the only shader I could find was orange... Does anyone know how/have a shader that will produce this effect? I know how to get the light brush in Radiant but I'm new to shaders. I do have a shader for my map and it is in shaderlist.txt.

Just in case it's still of interest, you need to create a brush, which is shaped like the one on the picture and select the texture common\gradient. There are textures with different colors and styles as well.